CHICAGO — After years of protests by Native Americans and pressure from the N.C.A.A., the University of Illinois in 2007 retired its mascot, Chief Illiniwek, who wore a feathered headdress and beaded buckskin to dance while the band played. The end of the chief, a university official said at the time, was a chance to “move our institution forward.”

Yet more than a decade later, an unofficial Chief Illiniwek still makes appearances around campus. Anti-chief protesters blocked a homecoming parade last October. And just last week, a professor opposed to the mascot was arrested at the campus basketball arena after searching in a bathroom for Chief Illiniwek.

Major League Baseball announced this week that the Cleveland Indians would stop using the team’s cartoonish Chief Wahoo logo on uniforms next year, but similar moves by professional teams and colleges around the country in recent years have rarely proved to be simple or absolute. Decisions to end the use of Native American imagery out of concerns about perpetuating racist and offensive stereotypes have run up against protracted battles with alumni groups and fans, who say they are attached to their team’s symbols and often insist that they are intended to honor indigenous people.

And here in Illinois, Chief Illiniwek has retained a stealth role on campus for years, neither officially sanctioned nor altogether gone. Though most of today’s undergraduates were in elementary school when he was formally retired, the chief has maintained all his power to impassion and infuriate.

“I think the people within the university were hoping the issue would just go away,” said Ivan Dozier, a former Chief Illiniwek and a board member of the Honor the Chief Society, which wants to restore the mascot’s official role. “I think that’s made things worse on campus.”

Mr. Dozier said he and the current Chief Illiniwek were in a bathroom last week at the State Farm Center, the basketball arena on the Champaign campus, during the most recent and most peculiar flare-up in the long-running debate.

Jay Rosenstein, a professor of media and cinema studies at the university, who once made an award-winning documentary about opposition to native mascots, had been scouring the arena trying to find and film the latest unofficial Chief Illiniwek. When Mr. Rosenstein recognized Mr. Dozier and saw him heading toward a bathroom, he followed him inside, figuring Chief Illiniwek might also be there.

“I was done with the urinal, headed over to the sink, and at some point I look up and there’s Jay Rosenstein at the end of the bathroom with his camera rolling,” Mr. Dozier said in an interview.

They argued. Security guards arrived. Soon Mr. Rosenstein, 57, was handcuffed and hauled to jail by a campus police officer.

“I was only a couple steps in — never even advanced past the sink area,” said Mr. Rosenstein, who was jailed on suspicion of unauthorized video recording but released the next day when the county prosecutor declined to file charges.

Julia Rietz, the state’s attorney of Champaign County, said in an email that her office had in the past pressed charges in cases that involved cameras hidden in bathrooms or locker rooms “to record unknowing victims for the offenders’ sexual gratification.” Ms. Rietz added, “While the arrest was technically appropriate, there was no evidence of such intent here.”

Mr. Rosenstein insists he never filmed anyone undressed, and said he was acting as an investigative journalist. He said he wanted to see if university employees were helping the chief to appear at the basketball game, which, he said, would be “a very big story.”

The incident has added fuel to a larger fight that seems far from over. Mr. Rosenstein was placed on administrative leave pending an internal investigation, prompting dueling calls for him to be fired and to be reinstated. Chief Illiniwek supporters touted plans to “stand together and show how many of us there really are” at a basketball game later this month.

“There will be some discourse at that event,” said Raneem Shamseldin, the student body president, who helped organize the protest of the chief during the homecoming parade.

“That’s not a threat. That is a promise.”

Though changing a Native American nickname or mascot almost always sets off debate, some institutions move on. At the University of Louisiana at Monroe, where sports teams known as the Indians were renamed as the Warhawks more than a decade ago, the issue long ago faded from the headlines. Lisa Miller, an administrator, said the new name was popular and that some current students might even be unaware of the old one.

“It’s difficult for a university to have a mascot that you can’t 100 percent embrace,” Ms. Miller said. “You’re always being cautious about doing things that may be offensive to others.”

Suzan Shown Harjo, a Native American activist who has sought to get such nicknames and mascots changed all over the country, said Illinois might have had more success if it had picked a replacement mascot and dropped its nickname: the Fighting Illini. Instead, there is no official mascot. The team logo, once an image of the chief’s face, is now an orange letter “I.”

She said the Cleveland Indians should also have gone further by changing the team name instead of just removing Chief Wahoo from uniforms.

Here in Illinois, the chief’s vehement opponents and steadfast defenders seem to agree on one thing: They believe the university’s leaders have repeatedly failed to act decisively on Chief Illiniwek, making matters worse. A university spokeswoman did not respond to multiple requests for an interview with an administrator.

Mr. Dozier, the former Chief Illiniwek, said everyone ought to be able to air their views more openly on campus. He said some people on both sides of the debate had become “more passionate” and “more ignorant” about the chief in recent years — a potentially “dangerous combination,” he said.

Mr. Rosenstein, the suspended professor, said Chief Illiniwek and its history were like “a bullet wound to the University of Illinois.” He called for the naming of a new mascot.

“A bullet wound can’t heal if you just put a Band-Aid over it,” he said. “You’ve got to go in there. You’ve got to dig around.”

A version of this article appears in print on , on Page A13 of the New York edition with the headline: At Illinois, a Sports Mascot, and a Controversy, That Just Won’t Go Away. Order Reprints | Today’s Paper | Subscribe